Lubricating powder pressed compact



May 29, 1951 a. w. WEBB LUBRICAIING FGWDER PRESSED COMPACT Filed Aug. 6, 1949 Patented May 29, T951 LUBRIGATING POWDER DRESSED COMPACT GeorgeWarren Webb, Revere, Mass, assignor by mesneassignments, to Isthmian- Metals, Inc., a corpora-tion of: Massachusetts ennlica eaAugustfir1 9 .Seri 5.- Claims. (01. 117-109) This invention relatesto; the art 0t powder metallurgy and especially to a method: of 'producing perfectly formed powder metal pressings at high diepressures.

In making powder metal pressings in which ferrous powders-are employed together with carbon and other alloys, toproduce very dense metal products having characteristics simulating steel, two pressings are generally desirable, an initial pressing up to as much asforty tons per square inch anda final pressing of from forty tons per square inch up to one hundred tons per square inch. Difficultiesare encountered when pressing at the higher pressures due to rapid die wear and seizing of the metal of the compact on the walls of the die, making it impossible to eject the compact without partial or complete destruction of the compact and/or the die.

Objects of this invention are to eliminate the foregoing difiiculties in a simple inexpensive manner without requiring any modification of the existing die pressing equipment and with a minimum of additional equipment and processing.

As herein illustrated this'is accomplished by placing a quantity of singlepressed powder metal compacts together with a quantity of metal pellets coated with a thin film-of relatively dry soap of carbon.certainalloys. and .a. lubricant. such .as

in a receptacle without added free soap and tumbling them until a thincoating of relatively dry soap is transferred-from the pellets to the entire exposed surfaces of the compacts. The compacts may have holesitherethrough and surface irregularities such as cavities, recesses, undercuts, etc. Accordingly it is contemplated that the pellets will consist ofa mixture of steel balls of various sizes at least some of which are small enough to enter the smallest holes and cavities of the compacts. In some instances small cylindrical pellets having'sharp endsmaybe employed. In accordance withthepractice of'the method the pellets are coated with a substantially dry film of soap by first dipping them in a water solution of soap and then drying them and the tumbling is carriedout in a cylindrical container which is turned end-over-end in contradistinction: to rotation about itslongitudinalaxis.

The method in its-various aspects will now be described in: greater detail-with reference to the accompanying drawings in which Fig. 1 is a diagrammatic view of a suitable equipment for tumbling'thepowder metal compac nd-t e oat d pellets:

Fig. 2 illustrates a number oficompacts in cross section havingv holes.- theretl'irough and/or recesses in their surfaces;

Fig. 3.. illustrates a number of difierent size spherical: pellets for receivinga-coating' of lubricant;

stearic acid, initially. pressing? the. mixture up, to approximately forty. (54,0), tonsper square. inch, sinteringthe compressed comp ct. to expellthe lubricant. to. withdraw thework hardening. and toprovide a cqherentcompact, and. then. repress, ing. or coming the compactat uptoone. hundred (1.0.0) tons. pen square. inchito provide. a product which is..very dense. and-which has. properties analogous to the top grade steels madeaccording to,conventionalprocesses.. The. first pressing does not give. much. trouble. because at. that. time the lubricantis, stillpresent. in. the. mixture. the iron and carbonhavenot combinedtogether with the hardening alloys. if. these are. present, to. form hard abrasive particlesand. the pressures. used arecomparatively low... Eollowingthe. first. pressmg, however, the. compacts are sintered which drives off the lubricant. and. if carbon is. present changes the iron tosteelby dissolving of,. the carbon and. alloys... therein. 'Ilhese. compacts bens ard. an abrasive. in character. when. subjectedto the second ressing. of. the. order of. 6.0.to 190 tons per square inch producesevere, die wear and frequently seize on the diewallsso that. it. is nearly impossible to ejectthem from the dies without destruction. of the compacts. and/or the dies. Accordingly. many, attempts have been made to lubricate the dies and the compacts prior to the second, e n Mo t suc prior at.- tempts haye..been inadequate. for onereasonor another especiallythe use of a .lubricant applied to the porous; compactitself because it enters into the pores of the compact-and duringthe sec,- ond pressing severely inhibits pressing to high densities since the lubricant" cannot get out and so;becomes;included within pores of the compact.

In accordance. with the novel aspect of the present invention the lubricant is applied solely to the surface region of. the compact and. in such a manner that therewill be no substantial penetration so that during the second pressing there will beno extraneous-matter occupyin the pores of'jthecompactwhich will take up space and generally render it impossible to compress the compact to the desired'h-igh density.. This is accomplished herein by" taking a quantity of metal pellets I0, Fig. 3, such as steel ballsor-small the compacts.

cylinders l2, Fig. 4, or a mixture of these, treating their surfaces so that they are smooth and clean, and dipping them in a solution of soap in water. A common variety of white soap is as good as any and when heated to a temperature of 150 F. such a solution will be fluid, but sufficiently gelatinous so that when the balls or cylinders are dipped therein they all pick up a coating of the solution. After dipping the pellets in the soap solution they are withdrawn, drained and placed in an oven wherethey are baked for several hours at about 150 F. so as to drive off moisture and leave a thin relatively dry film of soap M on their surfaces as shown in Fig. 5. The precoated pellets are then placed in a container l6 together with a quantity of compacts l8.

and the container is rotated to tumble the compacts and pellets. For best results the container is cylindrical as shown in Fig. 1 and is turned end-over-end about a horizontal axis 20 rather than about its longitudinal axis. This produces a better tumbling action in that the compacts and pellets are more thoroughly mixed and where some of the compacts have holes 22 this type of tumbling is much more effective in causing the pellets to enter the holes and hence to apply a coating to the inside surfaces of the holes. The compacts may have cavities 24 and/or undercut recesses 26 as well as holes. Accordingly, it is desirable to employ a mixture of pellets of several sizes (Fig. 3), some of which are small enough to enter the smallest holes or cavities in When the surface has very small indentations it may be desirable to use the cylindrical pellets [2 (Fig. 4) having sharp pointed ends which will enter such indentations and transfer the soap to the surface irregularities of the compact.

The tumbling causes the pellets to rub and strike against the compacts until a relatively dry soap film 28 is transferred to the surface of the compacts as shown in Fig. 6. It was found, for example, that approximately ten (10) pounds of pellets varying in size from inch to inch in diameter coated with soap would adequately lubricate about 2,500 cylindrical compacts /2 inch long, A; inch in diameter and having a A; inch axial hole therein before the pellets had to be recoated with soap. The tumbling was carried out end-over-end for 100 revolutions at the rate of approximately 30 R. P. M. By treating the compacts in this manner a. film of soap was applied to the surfaces of the compacts having a thickness of from .0002 inch to .0003 inch. Since no fluid is present, the coating is confined solely to the surface and there will be no appreciable penetration of the compact by fine soap particles or soap dust so as to fill the pores of the compact.

The foregoing film of between .0002 inch and .0003 inch affords excellent lubrication during coining in the ranges of sixty (60) to one hundred (100) tons per square inch.

The advantages of using a soap lie in the fact that at ordinary temperatures it is not a liquid and hence will not seep or penetrate into the porous surface of the compact thus filling it with extraneous material so that proper pressing cannot be obtained; that soap is unique among lubricants in its very high lubricating property, that soap is cheap and readily available, that it avoids the necessity of lubricating the die walls before each pressing cycle and finally that relatively dry soap will adhere to the compact much better than dry lubricants such as graphite or powdered soap.

I claim:

1. A method of applying a dry lubricant to the surface of a single pressed single sintered powdered ferrous metal compacts prior to a second pressing comprising dipping metal pellets in a soap solution, withdrawing the pellets and drying them to drive off the moisture and produce a relatively dry film thereon, placing the coated pellets together with the compacts in a container and tumbling them together until the surface of each compact is coated with a film of dry soap.

2. method of applying a dry lubricant to the surface of a single pressed single sintered powdered metal pressing comprising dipping steel pellets in a solution of 10% pure soap and water and at approximately F., removing the pellets from the solutionjand drying them in an oven at 150 F. for a suflicient length of time to drive off substantially all of the water and to provide a relatively dry film on the surface of the pellets and tumbling the pellets together with the pressings until the latter acquire a thin film of relatively dry soap on their exposed surfaces.

3. A method of applying a dry lubricant to the surface of powdered metal pressings, having external and internal surfaces, comprising selecting a quantity of metal pellets at least some of which are of smaller dimensions than any of the inside dimensions of the internal surfaces, dipping the pellets in a soap solution, withdrawing the pellets and drying them to drive off the moisture and produce a relatively dry film thereon, placing the coated pellets together with the metal pressings in a container and tumbling them together to coat the internal and external surfaces with a film of dry soap.

4. A method of applying a dry lubricant to the surface of a pressed powdered metal article without penetration thereof below the surface, comprising selecting a quantity of pellets of mixed sizes and shapes, some of which are spherical and others of which are cylindrical and have conical ends, dipping the metal pellets in a soap solution, withdrawing the pellets and dry ing them to drive off the moisture and produce a relatively dry film thereon, placing the coated pellets together with the articles in a container and tumbling them together to coat the surface of the articles with a film of dry soap.

5. A method of applying a substantialy dry lubricant to the surfaces of powder pressings which have external and internal surfaces and which have an inherently porous internal structure, without penetration of the lubricant below the external surfaces thereof, comprising selecting impervious, smooth-surfaced pellets of mixed sizes and shapes, applying soap to the surfaces of said pellets by dipping them in a soap solution, withdrawing the pellets and drying them to drive off the moisture and produce a relatively dry film thereon, placing the coated pellets together with the powder pressings in a container and tumbling them together to coat their surfaces with a film of dry soap.

GEORGE WARREN WEBB.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number 

